Position Sensitive Proportional Counter (PSPC)

Description

The position sensitive proportional counter (PSPC) was a thin-window gas counter. Incoming photons were absorbed, producing an electron cloud proportional to the photon energy. The electron cloud drifted to the anode wire grid where a high voltage was applied. In the high electric field, close to the wires, gas amplification of about 50,000 took place producing a charge signal at the anode wires which was proportional to the energy of the incoming photons. Simultaneous charge signals were induced in two cathode wire grids close to the anode. These signals were used to obtain the position of the photons with an accuracy of about 120 micrometers. A rotating filter wheel, in front of each PSPC, allowed the selection of reduced photon energy bands. In one position, the filter wheel was utilized as a vacuum door containing three radioactive sources for calibration.